LANGUAGE IN INDIA

THE NEUROLINGUISTIC PERSPECTIVES OF
LANGUAGE ACQUISITION, LATERALIZATION AND BILINGUALISM
A REVIEW
Shyamala Chengappa, Ph.D.
Sapna Bhat, M.Sc. (S&H)

Abstract

A resume of the current state of research on neuropsychophygiology of language is presented in this paper. The issues discussed are Lateralization for language, language acquisition, critical period for language Lateralization and development, controversy over left versus right hemisphere processing for language functions, cortical representation in bilingualism, evidence for neural organization, evidence from aphasia, evidence from language impairment and recovery, types of bilingualism and interference and bilingual aphasia. Trends as well as schools of thought are identified and critically examined. A need for studies in these areas in the Indian neuro-psycholinguistics is indicated.

1. Introduction

Currently there is more work and less agreement in neurolinguistics. The results of neuropsychophysiological research investigations are often contradictory. To make a comparison of these studies which generally lack uniformity is an exacting task.

The studies differ in terms of the variables under examination, experimental tasks, methodological procedures, criteria for subject selection, measures employed for testing, scoring and analysis, etc. Occasionally even with uniformity in the above, the results are conflicting.

The major causative factor for the disagreement and conflicting results could be the lack of amenability of brain processes to experimental control. Experimental control is very easily exercised, in comparison, on environmental variables. Accordingly, in spite of vast and intensive research and consequent varied evidence, it is still very difficult to conclude as to what part of the brain controls and to what extent, a certain human behaviour such as language.

Also this non-agreement on the morphology of the cortical structures and the functions subserved by them is an indication of the very complexity of the human behaviour, in relation to its neurophysiology. This has led to Whitaker's (Whitaker 1971) observation that the only thing that is certain is that language is represented in brain. Research in science, however, does not stop at these uncertainties and it should go on, with empirical data and systematic exploration towards controlled generalizable interpretations, with the hope that at one time in the not so distant future the studies would have covered the major steps towards the ultimate truth.

There is a great amount of literature, rapidly expanding too, on the maturation of the central nervous system focusing on the ontogeny of speech and language. Language is said to be lateralized to one of the hemispheres and, more commonly, to the left than to the right hemisphere.

Various tests are availed to determine the dominant hemisphere for language processing. Some of them include reaction time studies, dichotic listening tests, tachistoscopic viewing technique, the wada technique, etc. Averaged evoked potential techniques have also been added to the repertory. Biochemical, electrophysiological and morphological criteria are all availed of to draw interpretations concerning the neuropsychophysiology of language.

In what follows, we propose to give a brief resume of the latest research in some areas of neurolinguistics focusing on the language components and brain, Lateralization, language and left versus right hemisphere, language acquisition and critical period, cortical representation in bilingualism, evidence for the neural organization, evidence from aphasia, evidence from language impairment and recovery, types of bilingualism and interference and bilingual aphasia.

From this list it would be evident that this review/resume could only be too brief and would serve only to inform the uninitiated with the barest minimum.

2. Indian Linguistic Situation: Lack of Empirical Studies

In Indian linguistics, there have been very few studies exploring language functioning in relation to neural representation. There have been a few dissertations in speech and hearing and one in neurology that deal with some aspects of cortical processing and language, experimenting with non-invasive and psycholinguistic tools (Thirumalai and Subramanyaiah, 1979; Karanth, 1980; Chary, 1980).

There have also been a very few publications such as that edited by Ganeshasundaram and Radhakrishna (1981) which is a collection of papers on language teaching and cortex. Most of the scholars who have contributed to this edition have observed rightly the relevance of the study of cortical and neural processes to an understanding of human ability for language production, comprehension and use (Thirumalai 1981, Subramoniam 1981, Krishnamurthy 1981). However, very few of these studies have been based on empirical data.

With the rapid advance of neurosurgery and with an awakened awareness of linguists towards an understanding of the inevitability of neurological explanation of language processes, it is high time that more and more Indian linguists take more than a cursory glance towards the interdisciplinary area of human language and human brain.

3. Language Components and Human Brain

It is generally observed that the different levels or components of language are differentially distributed in brain with respect to their structure and function (Whitaker 1978).

Various localizationistic and functional models of brain have proposed. The recent view is indicative of a combined approach. It has been found that different parts of the brain, each small in area, subserve a particular function and that damage to certain areas of the brain result in certain deficits in language functioning.

The different cortical structures contribute differently to total language performance. Whitaker (1978) terms it as "performance grammar", the components of which are differentially distributed in the brain. a small area in the brain subserves several functions and a single function is contributed by a number of such small areas.

This simple observation would indicate the intricacy and the complexity of the brain mechanism in relation to human behaviour.

Small areas in frontal, parietal, temporal and occipital lobes are responsible together for language function and most part of the cortex does not contribute to performance grammar. The classical zones like Broca's and Wernicke's areas, supramarginal gyrus, angular gyrus and other motor and sensory cortical structures are responsible for functions like speech, audition, reading, writing, etc.

The evidence for differential distribution of language components comes from studies on individuals with brain damage who exhibit a dissociated linguistic disability. Some present a linguistic picture of deficient performance at the syntactic level and/or at the semantic level or at the lexical level where the problem may be either in the use of content words or function words depending on some crucial factors.

Any modality or language skill among the four important ones could be disturbed at the central level. Even within the modalities, there might be a differential picture of the two languages of a bilingual. For instance, within the broad category of writing, an individual can present a dissociated disability between the phonetically based writing systems and visually based one thus indicating a differential localization of the two writing systems (Sasanuma, 1975).

There are cerebral Lateralization measures that suggest that asymmetry in hemispheric dominance could be brought about by language-specific factors. Particularly strong is the evidence that different orthographic system (Syllabic or alphabetic versus ideographic) left to right versus right to left may enhance different cerebral organization (Albert and Obler 1978).

4. Lateralization

The concept of Lateralization is highly vague and is a matter for a great amount of speculation.

1. What exactly is Lateralization?
2. Is it genetically predetermined or controlled by environments?
3. To what extent is the nature versus nature principle appropriate?
4. When does Lateralization begin and when does it end, if the process has an end at all?
5. Can the completion of Lateralization be quantitatively measured?
6. Is there a "critical period" for Lateralization?
7. What is its duration?
8. Is the critical period same for all individuals, what are the factors that are important in any deviance?
9. Can there be a critical period independent of environmental stimulation?
10. How much of an effect does environmental stimulation?
11. How much of an effect does environmental stimulation, or genetic predisposition for that matter, have on the Lateralization process?

These are a few of the host of questions that plague a neurolinguistic introspection. None of these questions seem to have found an accurate explanation to quench the need for further exploration. In the following sections, the available data has been scanned, though not extensively in an attempt at gaining insight into some of these problems.

5. Left versus right hemisphere

The left hemisphere, rather than the right, is considered dominant for language functions in majority of right handed humans, Schnitzer (1978) asserts that the left hemisphere, rather than the right hemisphere, is endowed from birth with a greater facility for learning certain crucial aspects of natural language.

Neuroanatomical evidence is offered by many for left hemisphere preference. Geschwind and Levitsky (1968) report the presence of a larger temporal planum (the area behind Heschl's gyrus) in contrast with the right temporal planum in hundred adult brains. In addition, the neuroanatomical evidence for prenatal and paranatal asymmetry has also been reported.

Wada, Clarke and Hamm (1975) find evidence of morphological asymmetry of both the temporal planum and the frontal operculum (adjacent to Broca's area) in the twenty-ninth week of gestation, when those of the left hemisphere are found to be larger than those of right hemisphere in 90% of the adults and fetuses. This has been supported by many, thus erasing the notion that Lateralization is a function of language or that there is a strict cause and effect relationship between the two.

In addition to such neuroanatomical asymmetry, behavioral asymmetry has also been widely reported. Dennis and Whitaker (1976) studied the linguistic abilities of 10 year old children with complete hemisphererctomy prior to 4 ½ months of age. The isolated normal left hemispheres and the isolated normal right hemisphere of matched groups were compared along various phonological, semantic and syntactic tasks. Syntax seemed to be the most affected in left hemispherectonized individuals. On the basis of the findings it was concluded that the right hemisphere was deficient in the following abilities:

1. Understanding language auditorily especially when meaning was conveyed by syntactic diversity.
2. Detecting and correcting error in surface structures.
3. Repeating stylistic variation of sentences.
4. Forming tag questions from presented statements.
5. Determining sentence implications.
6. Combining syntactic and semantic information for replacement of missing pronoun, and
7. Judging the relationships among words in sentences.

It was noted that the right hemisphere was less endowed hierarchical abilities rather than any lack in its conceptual and/or semantic abilities.

The right hemisphere was viewed as being holistic, spatial, gestalt, synthetic, simultaneous, continuous, context dependent a positional and time independent where as the left hemisphere is viewed as analytical, verbal, logical, sequential, categorical, context independent, prepositional, time dependent by many (Galloway 1981).

Schnitzer (1976) argues that phonology is not so closely embedded in language structure as other linguistic aspects. This was in view of the finding that while children learn or acquire language(s), they do so without a foreign accent whereas most of the adults learning a second language would retain their mother tongue accent in the newly acquired language. Schnitzer (1978) is also of the opinion that, of all the linguistic components, phonology can be mastered by the right hemisphere to a relatively comparable level as the left hemisphere. One can infer from all these findings that right hemisphere is capable of processing some of the crucial language aspects.

6. Language acquisition and critical period

It is known that language acquisition is a natural process of mastering a language that requires a certain level of cortical maturation and hemispheric Lateralization, which in itself is an on going process. A biological barrier is erected guiding the quality of language acquisition before and after the critical period in specific ways.

Penfield and Roberts (1959) and Lenneberg (1967) conceived of Lateralization as the dominance of the left hemisphere over the right (and in some, the reverse) that place in the course of a chronological continuum and was completed within a specific period. The process of Lateralization and the critical period were considered simultaneous and both were considered to be conterminous around puberty.

The age at which Lateralization takes place is still a matter of wide controversy. One major record widely found is that Lateralization does take place in childhood. One of the supporting notions is that cerebral Lateralization for language(s) acquisition is not complete until the age of nine - twelve years (Penfield and Roberts 1959). However, this has been widely refuted.

Lenneberg (1967) asserted that language Lateralization was complete by 11-14 years. Krashen (1973) cited evidence that language Lateralization was complete by age four or five. Molfese (1972), and Molfese, Freeman and Palermo (1975) found evidence to support that Lateralization took place at birth or even beyond. Baser (1962) studied 102 cases of hemisplegia of early onset. He concluded that language Lateralization occurred early, be it to the left or right, and that both the hemispheres participated in language processing before the Lateralization was complete.

Thus, the only certainty until now, and the traditional view, was jeopardized with the advent of the proposal that Lateralization was present by birth. This fact would cut at the roof of the simultaneity notion of Lateralization and critical period. Lateralization, if present at birth, would, thus remain independent of the so called critical period.

Critical Period

Critical period was viewed as the congenial period for language acquisition when the child's brain is highly receptive and plastic. However, this traditional idea of the critical period is undergoing a radical change with the advent of recent studies which argue that there are multiple critical periods instead of only one. Those critical periods are actually states of plasticity of cortical structures for acquisition of certain functions.

The new interpretation (Seliger, 1978) given to the Lateralization and critical period concepts is that Lateralization is a continuing process which stretches much beyond the time span specified by Lenneberg (1967) and others.

In this interpretation, the term "critical period" refers to the gradual loss of plasticity in various parts of the brain for different functions over most of one's life time. In this light, Lateralization effects are those of both intra and interhemispheric nature. The evidence for Seliger's (Seliger 1978), multiple critical period hypothesis stemmed from age dependent aphasia and universal second language inabilities which were taken to be indicative of both the state of localization process and the gradual loss of plasticity.

Plasticity

According to Schnitzer (1978), although upto some point of development, the brain is "plastic" and "transfer" from left hemisphere to the right hemisphere is not done as proficiently as it is done by the intact left hemisphere. Schnitzer further remarked that although the brain is lateralized for language functions from before birth, it is relatively "plastic" for the first 5 years of life so that language could be shifted to the contralateral hemisphere in the event of neuropathology during this period. He later again asserted that the brain is never completely "plastic".

What Can We Infer From These Studies?

One may infer from the majority of the studies that traces of Lateralization are present prior to or at birth and that the brain is more plastic in the first few years of life than later to the extent that cortical structures can change and assume a function different from the originally intended ones in the event of pathology to the predetermined areas in the cortex and perform well, though not to the same extent managed by left hemisphere.

Disuse of certain areas for a long time would naturally preclude the revival of the functions to the original extent. Thus, probably, the previously uncommitted or differently committed right hemisphere could be less capacitated to start all over again with a new function. However, we notice in normal right hemisphere dominant individuals from birth that there is normal performance equivalent to the left hemisphere functioning.

Literacy Skils

Literacy (reading and writing) skills are said to enhance left hemisphere dominance. Even in an adult second language learner the left hemisphere might plat a major role although in the initial stages the right hemisphere may participate. State of acquisition, manner and modality of acquisition are observed to be important variables in the cerebral organization of L2 in the adult second language learning (Galloway 1981).

A controlled comparison of child and adult second language performances would yield some information on the strategies adopted and the cerebral organization in second language performance. A comparison of matched groups with and without current formal schooling (where reading and writing skills are emphasized) would also help in this venture to understand the extent of contribution of literacy factor in hemispheric Lateralization.

7. Cortical representation in bilingualism

There have been numerous studies which suggest that bilingual's two languages are represented bilaterally, one language in each hemisphere, and some studies that suggest that one language is represented in the left and the other bilaterally.

Penfield (1965) attributed the lack of confusion between the two languages in a bilingual's language behaviour to a switch mechanism that enables the bilingual to shift easily from one language to the other without confusion, without translation and without a mother tongue accent.

Earlier Potzl (1925) had hypothetically located the switch mechanism in the lower parietal region of the dominant hemisphere. They also reasoned that, if this part of the brain was injured, the bilingual could no longer shift freely from one language to the other; the bilingual either perseverated in either of the two languages or got them confused.

The notion that each language is stored n a different location in brain evoked a wide controversy. Potzl (1925) denied the existence of a separate centre for each language. Minkowski (1927) insisted that different languages were represented in a common area of the cortex, Veyrac (1931) and Ombredane (1951) accepted that there was no special locus in the brain devoted to foreign languages.

Finally Penfield (1953) and Penfield and Roberts (1959) categorically denied the existence of separate neural mechanism for each language of a bilingual. They also maintained that there was a bilateral representation, that early bilingualism enlarged the cortical areas devoted to language and that the brain mechanism was the same whether one, two or many languages were learned.

A couple studies asserted that there was no evidence for anatomical separation of languages within the brain (Minkowski 1963, Gloning and Gloning 1965), although Lebrun (1971) still held the opinion that different languages or languages acquired differently tended to be subserved by cerebral structures that were to some extent different. Paradis (1977) denies the need for postulating a localized switch mechanism. In support of this view, Albert and Obler (1978) argued that a continuously operating monitor system utilizing many parts of the brain controls language processing in a bilingual.

Penfield's (1953) and Gloning and Gloning's (1965) observation that language is represented more bilaterally in bilinguals than in monolinguals found support in the clinical evidence on aphasia in bilinguals. There is reported to be a higher incidence of aphasia following right sided damage in bilinguals than that in monolinguals (Ovachrova, Raichev and Geleva 1968; Albert and Obler 1978). This suggested that probably language in polyglots and a broader, more dynamic and less lateralized organization.

It is known that, typically, all the languages of a bilingual or a multilingual are similarly represented in brain as in a monolingual speaker. There appears to be no need to hypothesize any special anatomical structure or function in the brain of bilingual as differentiated from a monolingual. The bilingual does not need any different mechanism to enable him to choose one language over the other at a given time from the one he needs to speak at all (Whitaker 1978). The non-dominant hemisphere, to reiterate Paradis (1977), may play a role in the language of some bilinguals, but it is capable of doing so in monolinguals as well.

In the few interesting cases where right hemisphere dominance is suggested it could be noticed that one or more of the following situations play the lead: left handedness or ambidexterity, early damage to the left hemisphere or postpubertal acquisition of the language in question.

While none of these situations could ensure a shift in hemispheric Lateralization of one or the other language, right hemisphere dominance is always associated with these in the studies reviewed. According to Whitaker (1978), even if language dominance shifts to the right hemisphere or if there is one language in the left and the other in the right hemisphere, the same areas corresponding to those in left hemisphere subserve the language functions. This again is only speculation, and does not reduce the right hemisphere involvement in bilinguals.

Some Important Hypotheses

Albert and Obler (1978) found in an extensive review of clinical studies, experimental evidence for differential cortical Lateralization in bilinguals. They came to the following hypotheses:

A Neurolinguistic Model of Bilingualism

Galloway (1981) presents a neurolinguistic model of bilingualism based on a review of studies. This includes the following observations:

1. The right hemisphere does not appear to be more involved in L2 than the L1 in the early stages of second language learning, neither during informal naturalistic acquisition or classroom L2 learning.
2. The right hemisphere may be more involved during the early stages of learning to read a different orthographic system of the L2 (e.g., English Vs. Hebrew).
3. The L2 may appear more left lateralized than the L1 in readers of an L2 and/or classroom L2 performer without communicative experience in the L2.
4. The separate languages of the advanced L2 speaker or fluent bilingual do not appear to be differentially lateralized with respect to each other.
5. Language in advanced L2 performers in an L2 environment and/or balanced bilinguals may be more bilaterally represented than language in the monolingual.
6. Balanced bilinguals may develop different hemispheric processing strategies for language as a result of age of initial exposure to the L2 (before age 6 versus after puberty).
7. Adult L2 speakers may preferentially adopt right (gestalt, inductive) or left (sequential, deductive) cognitive styles for L2 classroom performance.
8. Mental grammars (grammatical competence) of certain, specific languages do not appear to be governed more by the right hemisphere (than the other languages).
9. Certain socio-ethnic bilingual groups may appear less left-lateralized for language.

8. Evidence for the neural organization

Neurological constraints of bilingualism can be explained on the basis of three important evidence available to date.

The first is the evidence available from the studies on cortical maturation, critical period for language acquisiton and the cortical Lateralization for language.

The second is the realization that levels or components of language are differentially distributed in the brain structurally and functionally and that is to an amount modality specificity.

The third is the evidence from the brain damaged individuals, that there is little difference in the representation of languages in brain but with a few but extremely interesting exceptions (Whitaker 1978).

The former two lines of evidence have already been elaborated upon in this paper. In the following section the third evidence is considered.

9. Evidence from Aphasia

Cases have been reported in which individuals after cerebral trauma exhibited different patterns of important after recovery of their premorbidly used languages. The ployglot patient might be limited to speech in only one of his languages, might switch languages inappropriately, or might speak in an incomprehensible jumble made up on words and idioms belonging to different languages.

For instance, deficient writing in one of the languages may be seen whereas writing in other language may be intact: reading ability in one language may be lost whereas in the other languages it may be retained; oral comprehension of one language may be preserved as against the comprehension in the other, etc.

Penfield's (1965) hypothesized that, in early bilinguals, language tended to be represented bilaterally was favoured by many. Gloning and Gloning (1965) observed that right brain damage caused aphasia more frequently in polyglots than in monoglots. Moreover they observed that the polyglotic linguistic behavior was not always associated with the lesion of the lower parietal lobe thus denying the existence of a bilingual switch mechanism.

10. Language impairment and recovery

Typically in a balanced bilingual aphasic, both the languages are equally affected if the languages involved allow a linguistic comparison. That is to say that if the variables mentioned (to be elaborated later) allow a comparison, then the extent of language functioning affected will be equal in both the languages.

This probably points to a better establishment notion that a bilingual's cortical organization is no different from that of a monolingual. But there are some significant instances, i.e., the case reports which deviate from the usual, where the languages involved are differentially impaired and are selectively recovered and these form an extremely interesting part of the study.

These instances occur in a significant minority and suggest the possibility of involvement of other cortical structures either in the same hemisphere or in the right hemisphere.

Various theories of aphasia in bilinguals and polyglots have been put forward. These theories deal mainly with the impairment and recovery of languages after cerebral insult. In the following section only a few theories that have been recently tested and interpreted are mentioned.

Galloway (1978) tested the following two theories in the case of a heptalingual who presented a differential linguistic picture after a massive cerebrovascular accident: Pitress (1895) suggested a theory that language most frequently and extensively used prior to cerebral insult would recover first. Ribot's (1906) theory suggested that the earliest acquired language(s) would be most resistant to aphasic impairment and that languages acquired later would be most impaired. Galloway found that in the case exemplified, Pitres theory was applicable and that the language that was extensively used prior to the insult was the one that was recovered first.

Since the measures of language disability could also be measures of language recovery to a certain extent especially in the immediate postmorbid period, the types of recovery or the patterns of recovery form an interesting area of research in a bilingual. Paradis (1977) identified five common modes of restitution.

1. Synergistic: Recovery in all the languages of a multilingual is simultaneous, this kind of restitution may be of two types.

Parallel: All languages are similarly impaired and similarly recovered to a similar degree.

Differential: The languages are differently impaired; recovery occurs either at the same or at a different rate. The degree of recovery may be at the same rate for all languages.

2. Antagonistic: One language recovers to a certain extent first and it starts regressing when the other language begins to recover.

3. Successive: One language begins to recover after the other one has been recovered almost fully.

4. Selective: One or more languages do not recover at all or remain severely impaired.

5. Mixed: A mixed language or mutual interference between the languages is seen in the process of recovery.

Of these types, the synergistic recovery pattern seems to be the more common, and of which the parallel pattern is most common. Antagonistic pattern of recovery is seen to be least common. Successive recovery can also be seen in cases of selective recovery except that some languages do not recover at all. Whitaker (1978) classifies successive recovery as a type of synergistic differential group, the difference being apparently in the temporal order. The two types of synergistic recovery and the successive recovery can be explained along similar lines of natural recovery in a monolingual aphasic which includes type extent and location.

Among these, the coordinate, compound and subordinate trichotomy has been the most discussed (Weinreich 1953), especially so in the case of bilingual aphasics.

Weinreich (1953) maintained that a bilingual need not be completely coordinate one nor a completely compound one. The bilingual's two languages may stand in a variety of relationship with each other, ranging from an idealized perfect coordinateness to total compoundness or subordinateness with real individuals situated some where on the continuum, sharing in various degrees, parts of their linguistic systems with all three types.

Slightly in contrast with these findings, recently Albert and other (1978) thought it was more likely that certain systems (e.g. voice production, phonological perception, deep semantics) would be compound for all bilinguals, while other systems (e.g. lexicon and syntax) would be coordinate to a greater or lesser extent. It is useful to retain the theoretical distinction between coordinate, compound and subordinate bilingualism and it should be possible to ascertain the extent to which and possibly the areas for which each bilingual is coordinate, compound or subordinate, by experimental investigations.

Jakobovits (1968) introduced the concept of degree of bilingualism into the coordinate-compound distinction, the proficiency level which is more a function of the amount of competence in each language than the type of bilingualism.

Lambert and Fillenbaum (1959) stated that coordinate bilingualism would posit more functionally separated neural structures underlying the two languages than would compound bilingualism. This suggested that languages which are learnt differently may be to some extent subserved by different neural substrates. Accordingly, after cerebral insult, languages which have been acquired in a compound way should be equally affected in aphasia, while languages which have been acquired in a coordinate way should be selectively impaired (Lebrun 1971).

More recently, according to Paradis's (Paradis 1977) types of restitution, it was supposed that parallel recovery or equal restitution of both the languages in bilingual aphasics, proportionate to the degree of proficiency in each language, was consistent with the notion of compound bilingualism as well as coordinate bilinguals. On the first line of reasoning, if the basic linguistic rules are affected the two lexical systems are also affected and on the second line of reasoning, there is equal disturbance because of the supposed single anatomic representation for both the languages (Whitaker 1978). In the same frame posited, the cases of differential recovery and selective recovery would support the notion of coordinate bilingualism (Wald 1974). The subordinate type is difficult to be explained on the type and amount of available evidence. There is no way, for that matter, at present to prove (or disprove) any of these theories.

11. Interference and bilingual aphasia

Mutual inter language interference is a common phenomenon observed in normal bilinguals. Interference is the use of features belonging to one language while speaking or writing another (Mackey 1970). The characteristics of degree of proficiency, function and alternation between language are detrimental to the type and amount of interference.

Weinreich (1953) observed that language mixing or interference occurred mainly at the semantic level and it was proposed to be the distinctive factor in the three types of bilingualism. Interference from first language to the second language was reported by many, due to bilingual imbalance in exposure and use.

Paradis (1978) reaffirmed that the interference occurred at the various strata along lines of stratificational grammar, viz., conceptual (concepts and their relationships), lexemic (grammatical elements like subject, verb, etc.), morphemic (radical, affixes, etc.), phonemic (phonemic elements like stress, clusters, etc.), phonetic (voicing, nasalisation, etc.) stratum.

Aphasiologists have observed that mixing or interference is a feature of bilingual aphasia as well. Selective mixing or compounding at various levels of language has been cited from the available literature by Paradis (1978). The aphasia in polyglots is reported to have presented language mixing at the levels of words or lexemes, phonemic level, prosody characteristics, graphemic, morphemic and semantic levels. Language mixing after cerebral insult in a bilingual is observed to be different from the picture presented by a normal bilingual. However, this has not been elaborated upon in the scanty literature available on the topic.

12. Factors responsible for

Several factors may contribute to the language disability and recovery pattern in bilingual aphasics.

1. Cerebral dominance for language
2. Locus of the lesion
3. Extent and severity of the lesion
4. Learning contexts (manner of acquisition)
5. Age of language acquisition and the age of cerebral insult
6. Order of acquisition of the two languages
7. Primacy (mother tongue or not) of the language
8. Structural and functional differences between the languages
9. Visual element of the languages (as to whether it could be read and/or written)
10. Degree of premorbid proficiency in each language
11. Premorbid frequency of use of each language
12. Premorbid affective attitudes towards each language
13. Appropriateness (to the patient) of a language
14. Language processing styles
15. The language of the hospital staff
16. The language employed in speech therapy

Paradis (1977) found no consistent correlation among some of these factors and the patterns of restitution, thus convincing the obvious inadequacy of the present day research.

Several studies have tried to interpret the different recovery patterns observed in multilingual aphasics (Paradis 1977, 2001). The main issues at stake are the reasons why recovery patterns differ so much across patients and why a language recovers better than the other(s).

Pitres (1895) and other neurologists in the past century claimed that failure of a language to recover during the intermediate and late phases was not due to its loss, but rather to pathophysiological inhibitory effects caused by the lesion. Pitres had drawn this conclusion on the basis of a general assumption and some empirical studies. The general assumption was supported by several neurologists and presupposed that all languages of a bilingual or a polyglot subject were localized in common language areas (Paradis, 1978, 2001; Fabbro, 1999).

In conclusion, our knowledge of the organization of the bilingual brain is certainly more extensive as compared to the first monograph published by Pitres more than 100 years ago. However, many aspects of the organization of the bilingual brain are still unknown and further clinical research based on an appropriate methodology and future experimental studies, at both the Neuroanatomical and the physiological levels, will hopefully lead to more advanced understanding of language organization in the multilingual brain.

13. Conclusions

Almost all the aspects of cerebral organization of language acquisition and bilingualism are reported. Many of the studies reported lack information on all relevant issues, hence, precluding a direct comparison. Several methodological or variable are of a questionable nature. In the experimental tasks adopted one is not sure what exactly a particular task is measuring.

How is one particular task superior over the others and so why is it chosen? Can any laterality test provide information about the extent or degree of Lateralization which would be useful if available, for comparison on language tasks? Is the test for language functioning measuring that ability only/and/or something else also? Regarding cerebral organization, how substantial are differences between monolingualism and multilingualsm, if there is any? Are there significant differences in the neural organization and functional organization of bilingualism and multilingualism? Several such questions remain unanswered.

As mentioned previously, the degree of control of variables would pose several problems even at the level of basic specifications: age of acquisition, handedness, degree of proficiency, literacy level, etc. To talk about but one of the uncertainties there is the notion about cerebral Lateralization and handedness. The varying results of the studies so far, would imply that there is no one to one relationship, for sure, between the two. One does not determine the other (i.e. Lateralization and handedness). In the majority of the findings they coexist and in significant minority they do not.

Lack of matched groups, size of the sample, lack of controlled generalization, etc. are all differentially consequential in terms of interpretation of results reported.

The growing amount of evidence, however, is hoped to fill in the great many lacunae in the areas of cerebral dominance, hemispheric maturational difference, Lateralization for language, critical period, etc.

Studies on brain damaged, monolingual and multilingual, childhood and adult aphasics, correlation of normal developmental stages of language with cortical maturation would all help in understanding the neural substratum of language better, thus aiding in clinical speech and language rehabilitation and in the understanding of the limitations of theories of language proposed by various schools.

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